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The Middle Awash research project, which White co-directs with his Ethiopian colleagues Berhane Asfaw and Giday WoldeGabriel, announced its greatest good fortune last October: the discovery, 15 years earlier, of the skeleton of a member of our family that had died 4.4 million years ago at a place called Aramis, less than 20 miles north of today's Yardi Lake. Belonging to the species Ardipithecus ramidus, the adult female—"Ardi" for short—is more than a million years older than the famous Lucy skeleton and much more informative about one of evolution's holy grails: the nature of the common ancestor we share with chimpanzees. In the mediaphilic field of paleoanthropology, it has become almost a reflex to claim that one's new find "overturns all previous notions" of our origins. Tim White despises such hyperbole. But in Ardi's case, it seems to be true.

Sensational as it is, however, Ar. ramidus represents just one moment in our evolutionary journey from an obscure ape to the species that holds in its hands the fate of the planet. There is no single better place on Earth to see how this transformation took place than the Middle Awash. In addition to Aramis, layers there representing 14 other time periods have yielded hominids—members of our exclusive lineage (also called hominins)—from forms even older and more primitive than Ar. ramidus to early incarnations of Homo sapiens.

White had told me that many of these "windows of time" lie in such close proximity that one could literally walk from one to another in the course of a couple of days. He invited me to join the team in the field so they could prove it. Our plan was to begin in the present at Yardi Lake and walk backward through time, peeling away what makes us human, trait by trait, species by species.

Herto: The Ancient Familiar

I rode into the field with two dozen scientists and students and six armed guards. Our caravan of 11 vehicles carried enough food and equipment for six weeks. As we threaded through the highlands, sharply terraced fields of sorghum and corn gave way to misted forests. Th e road was littered with the flotsam of mere history—around a bend the burned hulk of an army armored personnel carrier from the civil war in the 1990s and, farther on, the eroded name “MUSSOLINI” carved in the lintel above a tunnel, a legacy of the Italian occupation of the country in the 1930s.

From the top of the escarpment we switchbacked down a gargantuan staircase formed as the Arabian continental plate pulled away from Africa beginning some 30 to 25 million years ago, dropping the Afar Basin ever deeper into the rain shadow of the highlands. As we descended, the vegetation grew thinner, the sun more intense. A few hundred yards above the basin floor, we pulled over. Below us the western hills in the foreground fell toward a ragged, fault-scarred plain. On the horizon to the southeast, beyond the green ribbon of the Awash River, the highlands seemed to merge with the cone of the young volcano Ayelu. Below Ayelu was a sliver of silver: Yardi Lake.

Two days later we were walking along its shore—White, Asfaw, and WoldeGabriel, along with two longtime members of the project, geologist Bill Hart of Miami University in Ohio and Ahamed Elema, the leader of the Bouri-Modaitu Afar clan. For a while we followed the lake margin, bright dragonflies flitting about our ankles. It was the perfect setting for making fossils, now as in the past. Animals come to eat, to drink, to kill and be killed. Bones get buried, rescued from decomposition. Over eons, water trickles minerals in, organics out. White—58 years old, hard and thin as a jackal—poked with his long-handled ice ax at things newly dead. A catfish skeleton left by a fish eagle beneath an acacia tree. The head of a cow, still wearing a leathery mask of dried flesh. "If you want to become a fossil," he said, "you can't do much better than this."

Our first day's walk would take us east across an uplifted finger of land called the Bouri Peninsula, toward the Afar village of Herto. We emerged from the shade of the lake fringe and crossed some low, gray sand dunes. Soon an Afar boy and girl came with their herd of goats to investigate. The Afar are pastoralists, and except for the addition of firearms, their lives today are not substantially different from the way they were 500 years ago. As we walked in the heat among the gently bleating animals, it was easy to imagine historical time rushing backward with every step.

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